ANTITARNISH, ANTIMICROBIAL COPPER ALLOYS

AND SURFACES MADE FROM SUCH ALLOYS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Utility Patent Application No. 12/943,196, filed November 10, 2010 and U.S. Provisional Application No. 61/259,837, filed on November 10, 2009. The entire disclosures of which are incorporated, herein by reference.

BACKGROUND

[0002] This invention relates to antimicrobial copper alloys, and to surfaces made from such alloys, and in particular to tarnish resistant antimicrobial copper alloys and surfaces made from such alloys.

[0003] Copper and copper alloys are known to have useful antimicrobial properties. These metals can kill human pathogens, including bacteria such as E. coli 0157, Listeria monocytogenes, Salmonella, and Methicillin-resistant Staphylococcus aureus (MRS A). The Environmental Protection Agency has declared that alloys containing 65% or more copper have inherent antimicrobial properties. See,

Antimicrobial Copper Alloys Group I (EPA Reg. No. 82012-1), Antimicrobial Copper Alloys Group II (EPA Reg. No. 82012-2), Antimicrobial Copper Alloys Group III (EPA Reg. No. 82012-3), Antimicrobial Copper Alloys Group IV (EPA Reg. No. 82012-4), and Antimicrobial Copper Alloys Group V (EPA Reg. No. 82012-5), incorporated herein by reference. [0004] Because of this antimicrobial property, copper and copper alloys would at first blush appear to be good candidates for fabricating surfaces in health care and food service facilities, and even in home and industrial settings. However copper's tendency to tarnish, which can be accelerated by the application of certain cleaners used in such environments, makes many copper alloys unsuitable for such uses. Tarnishing is psychologically and aesthetically undesirable for such surfaces, particularly in health care and food service institutions, where tarnished surfaces would appear unattractive and unclean. Furthermore, the distinctive copper color of many copper alloys limits their acceptability for some applications.

[0005] While some silver-toned tarnish-resistant antimicrobial copper alloys are known (e.g., C710), for at least some applications it is desirable to avoid silver- toned colors because these may be confused with more familiar silver-toned surfaces such as stainless steel, which while they can be sterilized, are not regarded as

antimicrobial. C706 is another tarnish resistant antimicrobial copper alloy, but has a rose color, which may not be desirable for some applications.

SUMMARY

[0006] A preferred embodiment provides alloys with a combination of antimicrobial properties, attractive appearance, and tarnish resistance. Generally, the alloys of this preferred embodiment comprise at least 1% Ni, and up to 3 % Al.

(Percentages are weight percentages unless otherwise indicated.) In a more preferred embodiment, the alloys have a golden visual appearance, and contain Zn and/or Mn up to about 15%. Other elements that do not negatively impact tarnish resistance or

antimicrobial activity of the alloy can be present.

DETAILED DESCRIPTION

[0007] Embodiments of this invention provide alloys, and surfaces made with such, alloys, with a combination of antimicrobial properties, attractive appearance, and tarnish resistance. In a preferred embodiment, the alloy has an attractive golden visual appearance.

[0008] Generally the alloys of this preferred embodiment comprise between about 1 and about 4 % Ni, and up to 3 % Al. (Percentages are weight percentages unless otherwise indicated.) In a more preferred embodiment the alloys contain Zn and/or Mn up to about 15%. Other elements that do not negatively impact tarnish resistance or antimicrobial activity of the alloy can be present.

[0009] As detailed below, the inventors have observed that Cu-Zn alloys performed poorly both in touch and cleaning testing compared with other alloys; but that Cu~Ni alloys performed very well in both touch and cleaning testing. Resistance to tarmshment by touching appears to be a more significant differentiator man other properties, such as resistance to cleaning agents and humidity.

[0010] Of the alloys that the EPA recognizes as antimicrobial, the inventors have found that alloys of Cu-Ni-Al provide a desirable combination of tarnish resistance and color, and that in particular alloys of Cu-Zn-Mn-Ni- Al, such as those identified herein as K475, K476, K589, K592, and K593 provide a desirable combination of antimicrobial activity, tarnish resistance, and a desirable golden visual appearance. Nickel

[001] ] In general, nickel is present in sufficient amounts to improve tarnish resistance. Generally, nickel in excess of about 1% improves tarnish resistance, and the nickel content is preferably at least 1.5%. In Cu-Ni-AI alloys the Ni content may be as high as 6.9% or higher. There is not necessarily an upper limit on nickel content, but nickel content is generally limited by its cost compared to the other alloying elements, and its effect, together with the other alloying elements, on the color of the alloy.

Aluminum

[0012] Aluminum improves resistance to tarnishment from touching.

Aluminum is preferably present in amounts up to about 3%. It is generally preferred that aluminum be present at a level of at least 0.6%. Additional aluminum above 3% does not appear to be necessary, and in amounts above about 8% to 11%, can negatively affect antimicrobial activity of the alloy. See, Use of Copper Cast Alloys to Control

Escherichia coli 0157 Cross-Contamination During Food Processing, Applied and Environmental Microbiology, June 2006, pp. 4239-4244, incoiporated herein by reference.

Zinc

[0013] Zinc, alone or in combination with manganese, improves the tarnish resistance of Ni-Cu and Ni-Al-Cu alloys, and affects their color. If zinc is present without manganese, then the zinc content is preferably at least about 6.8%, and preferably less than about 15%. If zinc and manganese are both present, zinc can be present in any amount, but it is preferable that the total content of zinc and manganese does not exceed a level which increases susceptibility to stress corrosion cracking, generally believed to be about 15%. Where both zinc and manganese are present, the zinc content is preferably between about 6.8% and about 10.8%. Considerations in setting the upper limit of the zinc content include resisting stress corrosion cracking, and maintaining desired color. Manganese

[0014] Manganese, alone or in combination with zinc, improves the tarnish resistance of Ni-Cu and Ni-Al-Cu alloys, and affects their color. If manganese is present without zinc, then the manganese content is preferably at least about 4.8%, and preferably less than about 15%. If manganese and zinc are both present, manganese can be present in any amount, but it is preferable that the total content of zinc and manganese does not exceed a level which increases susceptibility to stress corrosion cracking, generally believed to be about 15%. Where both zinc and manganese are present, the manganese content is preferably between about 4.8% and about 6.9%. Considerations in setting the upper limit of the manganese content include resisting stress corrosion cracking, and maintaining desired color.

Total. Zinc and Manganese Content

[0015] It is believed preferable to maintain the total content of Zn and Mn below a level which increases susceptibility to stress corrosion cracking, generally believed to be about 15%.

[0016] Experimental alloys (identified with prefix IC) for Examples 1-5 were prepared by casting into 10 pound laboratory ingots. Alloys for Example 6 were prepared by direct chill casting into 7 inch x 30 inch x 25 foot bars. The production bars and laboratory ingots were both processed to mill plate by soaking at about 850° C and hot rolling to between 0.5-0.6 inch thick. In each case, the hot rolled plate or coil was milled to remove surface oxides developed during hot rolling. The alloys were then processed to the condition in which they were tested by sequential cold rolling and annealing steps to produce the desired metallurgical condition.

Example 1

[0017] Eight commercial and four developmental alloys were subjected to cleaning, touch testing, and humidity testing.

[0018] The tested alloys (Table 1) were either as-rolled (AR) or roughened with Scotch-Brite® (SB).

Cleaning Testing

[0019] All the alloys were degreased with isopropyl alcohol before testing. The cleaners used, along with their respective measured pH, are given, in Table

[0020] All samples were wiped with a cloth saturated with the cleaner

(PA, WA, HP, and D) or sprayed (in the case of F), and wiped off twice daily with a minimum of 4 hours between cleanings for ten days. (Wex-All, which is a general disinfectant, was used at full strength and not according to the manufacturer's recommendation. At this strength Wex-All appeared to leave a film on the surface which could be readily removed with a 50:50 Wex-All solution. This film darkened over a period of several hours to overnight.) All tested alloys were judged by at least three independent judges according to the following criteria:

1 No discoloration

2 Less than 60% light discoloration

3 More than 60% light discoloration - no dark areas

4 Complete discoloration-some very dark areas

5 Majority is dark discoloration.

with lower scores being better than higher scores. The results are reported in Table 3A. [0021] In general, the more acidic cleaners had a much stronger effect on the alloys (particularly K444, K445, K451, and K453 and CI 10 and C230). These alloys contain either high Mn, and/or low Zn. It appears when comparing the C230 to the C260 that more Zn may be beneficial, while higher Mn may cause the alloy to be affected more strongly by acids. Alloy C638, with Al + Si was also significantly affected by the acid- containing cleaners.

[0022] Because CI 10 and C230 performed poorly in the first round of testing, they were eliminated from further testing, and the remaining eight alloys, together with standard 304LSS were tested. The tested alloys (Table 1) were either as- rolled (AR) or roughened with Scotch-Brite® (SB). All were degreased with isopropyl alcohol before testing. Diluted Wex-All (WA-d) and Purell hand cleaner (P) (see Table 2) were used. Both cleaners were wiped on 2 times daily at least 4 hours apart. The cleaners were not wiped off. All tested alloys were judged by at least three independent judges according to using a 3 point, rather than the 5 point scale identified above:

1 Unchanged

2 Light discoloration - non uniform

3 Light discoloration - uniform

with lower scores being better than higher scores. The results are given in Table 3B.

[0023] New composite cleaning scores for the alloys were determined combining the scores for some of the cleaners used in part 1 and the two additional cleaners used in part 2. These are shown in Table 3C.

Touch Testing [0024] Touch testing consisted of having a plurality of different people touch the samples of each of the alloys (except 304LSS) for 5 minutes twice daily for 21 days. Alloys were rotated among people each week for 3 weeks. All tested alloys were judged by at least three independent judges according to the following criteria:

1 Little if any discoloration

2 Light discoloring incomplete

3 Discolored more than 75 % but not deep

4 Deep discolored spots

5 Complete and deep discoloration with lower scores being better than higher scores. The results are reported in Table 4. Humidity Testing

[0025] Resistance to humidity was tested by placing samples of each of the alloys (except 304LSS) in a humidity chamber at 28°C and 95% humidity for 3 weeks. All tested alloys were judged by at least three independent judges according to the following criteria:

1 Slight water marking

2 Some water marks

3 Water marks no pits

4 Some pits with water marks

5 Many pits with water marks

with lower scores being better than higher scores. The results are reported in Table 5. [0026] The results of the three tests were compiled, and are reported in

Table 6 A. Of the development alloys, K451 was the best performing, with a total score of 18. K451 had the lowest Mn of the development alloys, and contained 3.75%Ni. The results using the new cleaning scores of Table 3C and the touch scores of Table 4 and humidity scores of Table 5 are reported in Table 6B.

Example 2

[0027] Two commercial and seven developmental alloys and stainless steel were subjected to cleaning, touch testing, and humidity testing. The tested alloys (Table 1) were either as-rolled (AR) or roughened with Scotch-Brite® (SB).

Cleaning Testing

[0028] All the alloys were degreased with isopropyl alcohol before testing. The cleaners used were Wex-All, diluted 1 : 128 with water (WA-d), Proxi® (HP), Fantastik® (anti-microbial) (F), and Dawn® Dish Soap diluted with water (1 : 10) (D).

[0029] All samples were wiped with a saturated cloth and wiped off

(except the diluted Wex-All and Purell®, which were not wiped off) in the morning and at the end of the day for 2 weeks. Images were recorded every day in-between cleanings. All tested alloys were judged by at least three independent judges according to the following criteria: 1 No discoloration

2 Less than. 60% light discoloration

3 More than 60% light discoloration - no dark areas

4 Complete discoloration-some very dark areas

5 Majority is dark discoloration.

with lower scores being better than higher scores. The results are reported in Table 8. With the exception of C425, all copper alloys tested were adversely affected by Wex-All. Alloys C425, K516, K475, K476, and K477 all performed at or very close to stainless steel (304L) in these cleaning tests.

Touch Testing

[0030] Touch testing consisted of having a variety of people touch the samples of each of the alloys for 5 minutes twice daily for 21 days. Alloys were rotated among people each week for 3 weeks. All tested alloys were judged by at least three independent judges according to the following criteria:

1 Little if any discoloration

2 Light discoloring incomplete

3 Discolored more than 75% but not deep

4 Deep discolored spots

5 Complete and deep discoloration

with lower scores being better than higher scores. The results are reported in Table 9. Humidity Testing

[0031] Resistance to humidity was tested by placing samples of each of the alloys in a humidity chamber at 28°C and 95% humidity for 3 weeks. All tested alloys were judged by at least three independent judges according to the following criteria;

1 Slight water marking

2 Some water marks

3 Water marks no pits

4 Some pits with water marks

5 Many pits with water marks

with lower scores being better than higher scores. The results are reported in Table 9.

[0032] K475 performed equal to stainless steel in both the touching and humidity tests. The other two developmental alloys, K476 and K477 both are very close in performance to the stainless. These alloys appear to be relatively unaffected by humidity or human touch in this testing. The combination of Ni + Al appears to be beneficial to resistance from tarnishing from touching and humidity, at least under these testing conditions.

Example 3

[0033] Several alloys were prepared (see Table 10), and their mechanical properties compared (see Table 1 1).

[0034] Table 12 collects the results of the testing from Examples 1 through 3. In particular, data for alloys K538 - K543 and alloys K589 - K602 comes from testing, in accordance with the procedures set forth in Example 2. In Table 12, alloys with clean test scores of less than 4.5 and touch test scores of 2 or less are indicated as having "good" tarnish resistance. [0035] Color information for selected alloys is also indicated in Table 12, based upon the following comparative scale:

As disclosed in co-assigned U.S. Patent No. 6,432,556 (incorporated herein by reference), color determination may be by spectroscopy or other objective means.

Instruments, such as provided by Hunter Associates Laboratory, Inc. of Reston, Va., quantify color according to a lightness attribute commonly referred to as "value" and two chromatic attributes commonly referred to as "hue" and "chroma". Hue is color perception, the recognition of an object as green, blue, red, yellow, etc. Chroma is color concentration and ranges from grey to pure hue. Value is the lightness of the color and ranges from white to black. One method of specifying color is by a CIELAB scale. CIE stands for Commission Internationale de 1' Eclairage (International Commission on Illumination) and LAB stands for the Hunter L,a,b scale. The CIELAB color chart expresses hue as a combination of an a* value and a b* value extending arcuately about the color chart, with +a* being red, -a* being green, +b* being yellow and -b* being blue. Chroma is expressed as a value from the center of the circle with the center (0) being grey and +/- 60 being full richness of the specified color. Value is expressed as an L* number ranging from white to black, such that the combination of hue, chroma and lightness represents a specific point on. a three-dimensional sphere and a specific color. [0036] Thus, alloys K513, K475, K475A, K476, K477, K589, K592,

K593, and K599 provide antimicrobial materials with good tarnish resistance. Further, alloys K475, K475A and K476 provides antimicrobial materials with good tarnish resistance and a whitish golden color, and alloy K477 provides an antimicrobial material with good tarnish resistance and a yellowish golden color.

[0037] Tables 13-15 show mechanical properties for some of the alloys in

Table 12.

[0038] Table 16 is a table of other possible antimicrobial, tarnish-resistant alloys, with desirable appearance and color traits.

Example 4

[0039] Alloys in Table 16, plus additional alloys were subjected to touch and cleaning tests (reported in Table 17). The sample preparation differed somewhat for these tests. The results in Table 17 were performed on samples which were polished smooth and degreased prior to testing, to remove surface imperfections in order to minimize test variables. Touch testing was done as before using a variety of people touching the samples of each of the alloys for 5 minutes twice daily for 21 days. Alloys were rotated among people each week for 3 weeks. All tested alloys were judged by at least three independent judges according to the following criteria:

1 Little if any discoloration

2 Light discoloring incomplete

3 Discolored more than 75% but not deep

4 Deep discolored spots

5 Complete and deep discoloration

with lower scores being better than higher scores. The results are reported in Table 17.

[0040] Samples of the same alloys were subjected to cleaning testing; again these samples were polished smooth and degreased. The cleaners used were, CleanCide Wipes (CleanCide), Proxi®, Fantastik® (anti-microbial) , and Dawn® Dish Soap diluted with water (1 : 10)). All samples were wiped with a saturated cloth and wiped off, except the in case of CleanCide wipes which were wiped on without being wiped off, twice daily in the morning and at the end of the day for 2 weeks. All tested alloys were judged by at least three independent judges according to the following criteria: 1 No discoloration

2 Less than 60% light discoloration

3 More than 60% light discoloration - no dark areas

4 Complete discoloration-some very dark areas

5 Majority is dark discoloration.

with lower scores being better than higher scores. Commercial alloy C752 was included as a standard. The alloy did very well through the testing.

[0041] None of the experimental alloys K603-K637 performed well with

CleanCide, but they generally performed well in the other cleaners and the touch tests. There are some slight differences within this group, such as alloys with lower Mn did slightly better than those with higher levels, .e.g, K610 versus K604.

* Alloys with the same numbers have the same compositions, but there are slight variations in the reported compositions due to improvements in measuring techniques.

Example 5

[0042] An alloy with composition of about Cu - 7.75 Zn -5.75 Mn - 2.5

Ni-1.5 Al would give good cleaning and touch results based upon the results of Example 4. A new series of alloys were cast, hot rolled HR75% (reduction in thickness), milled and cold rolled CR 92%, annealed under different conditions and given a small 1044% final reduction. The compositions and mechanical test results are reported in Table 18. Alloys in Table 18 were cleaned and evaluated as in Example 4. All alloys scored 1 when cleaned with Proxi®, Dawn® diluted with water(l :10), and antimicrobial Fantastik. As before, the alloys did poorly when cleaned with CleanCide wipes, rating 3-4.

Example 6

[0043] An alloy was cast at a production level of the composition, Cu

7.75 Zn - 5.38 Mn -2.51 Ni - 1.61 Al. The overall process used was:

HRP 93% 850°C→ CR 90-94%→ SA 750°C→ CR 10-12% Four items were made, one as-annealed the other 3 were one quarter hard (H01); i.e. rolled CR10-12%s. The plant trial results are given in Table 19.

Stress Corrosion Cracking (SCC) Testing

[0044] Due to the envisioned service conditions for this alloy, stress corrosion susceptibility testing was initiated in Mattsson's solution, in accordance with ASTM G37-98. Mattsson's solution is composed of copper sulfate pentahydrate, ammonium sulfate, and ammonium hydroxide in water. The pH is controlled from 7.1 to 7.5, the region of highest SCC susceptibility. Test specimens are examined periodically for cracks under a stereo microscope at 30x. A visible penetrating crack is judged a failure. In addition, the samples are evaluated for stress relaxation. If the remaining stress on the sample falls below 80% of the original stress level, the sample has failed. The recommended test duration in ASTM G37-98 is 1000 hours. It is customary to consider that survival of at least 1000 hours in this test indicates that the material is essentially immune to SCC. Samples of Item 1 (Table 19) as-received and with a relief anneal of 300°C/lh have been tested in Mattsson's solution. All three samples of Item 1 in the as-received condition completed the test without failure as did 2 of the 3 samples of Item 1 which were relief annealed. One sample of Item 1 with the relief anneal, failed at 648 hours. The cause of the failure is not known. The plant trial material is not susceptible to SCC in Mattsson's solution.

Color Analysis

[0045] All of the alloys plus the plant trial material was evaluated for color using, a standard condition; 10 degree observer using average daylight D65. The color measurement method is accordance with paragraph 35 in this document and is as described in US Patent 6,432,556, incorporated by reference herein Table 20 presents the results on the alloys from Tables 18 and 19. The terms in the table are L* is light to dark, C* is chroma, h* is hue, a* and b* are the locations on the plane in space defined by L*, C* and h*. These terms are further explained in

http://www.hunterlab.com/manuals/appendixa2 5 ,pdf incorporated herein by reference.. The dEcmc(l :c=2.0) is calculated from the color measurements and is used to compare color measurements. All alloys in Table 20 are compared to plant trial material. Note that there are no dEcmc(l :c=2.0)values over 1.1 therefore, all these alloys appear to have the same color to the human eye. Table 20 Color measurements using CIELAB scale. dEcmc(l :c=2,0) is used to compare

Antimicrobial Testing

[0046] Samples of Item 2 in Table 19 were tested for resistance to microbial growth. The test methodology used was based on ASTM 1153-03, "Standard Method for Efficacy of Sanitizers Recommended for the Inanimate non-Food Contact Surfaces". The materials were cleaned and degreased and inoculated with methicillin resistant staphylococcus aureus, (MRSA). Growth was monitored on the copper alloy and a stainless steel control for 1, 2 and 4 hours at 21°C. Triplicate samples were used in the study. The stainless steel control colonized additional bacteria as time progressed, no bacteria were found on any of the copper specimens at I, 2 or 4 hours. The inoculation and counting methods used were in accord with ASTM 1153-03. The copper alloy of Item 2 was demonstrated antimicrobial under the test conditions. Table 21 shows the percent reduction of MRSA over time on Item 2 (Table 19).

Nickel Release

[0047] Nickel can cause some people to have an adverse reaction. It is a desirable, but not necessary property that the alloy has low Ni release. Various methods of determining whether an alloy would release enough nickel to cause reactions in individuals with sensitivity to nickel are known. One such test consists of mixing solutions of dimethylglyoxime and ammonium hydroxide on the surface of the test article. If nickel is released, a light pink to red color results on the test article. Additional information about such testing is disclosed in http://corrosion- doctors.org/Allergies/nickelallergy.htm, incorporated herein by reference; and. in

Screening Tests For Nickel Release From Alloys And Coatings In Items That Come Into Direct And Prolonged Contact With The Skin, PD CR 12471 :2002 by British Standards Institution on ERC Specs and Standards.